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Heat Treat Oven Insulation Question.

Discussion in 'Heat Treating' started by Wuatt, Jun 10, 2021.

  1. Wuatt

    Wuatt New Member

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    Hey everyone! I'm currently building myself an electric heat treat oven, and I'm getting ready to weld the frame together. But before I do I have a question about insulation. I'm using standard K23 insulating fire bricks that I sourced from a local pottery supply store. Will they be enough insulation on their own? Or do I need to add a layer of 1" ceramic wool insulation as well?
    Thanks in advance everyone!
     
  2. Magnus

    Magnus Member

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    Hi Wuatt,

    I made my oven using K26 bricks and there's easily enough insulation to heat treat stainless. It does get hot on the outside if it's been on for a while but this is to be expected.

    I'll warn you that the K23 bricks that I've sourced from my local pottery store were very weak and cracked or broke very easily. I don't think i would try to build an oven out of those bricks but the ones you get may be different.

    Magnus
     
  3. Joelsund

    Joelsund Active Member

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    the k23 should be fine as far as insulation goes. Maybe just coat the outside in satanite or some other cement to give it a bit more structure, also coat the bottom on the inside so it doesn't get all scraped up sliding knives in and out.
    Also wouldn't hurt to cover it in kaowool. I did that with mine and it seems to heat slightly faster and the outside is only warm to the touch where previously with just the brick it would burn me if it touched it.


    scroll down for some specs on each type of brick https://www.global-refractory.com/k23-28-firebrick/
     
  4. Wuatt

    Wuatt New Member

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    Hey, thanks for the reply! I bought a case of K23 bricks from the same pottery supply store I'm using this time (Not too far away from Vancouver) when I built my small forge. They are very light and they are fragile enough that when dropped on a concrete floor they break into around 3 or 4 pieces. I purchased a couple of the K26 bricks online just to see if they would work better for building my oven, but I found they were extremely similar to the K23 bricks I had previously used, other than being slightly heavier and able to go up to 2600f as apposed to 2300f.
    Do you know of any place in the greater Vancouver area, or online I would be able to purchase the K26 bricks for not too much more than K23?
    I pay about $6.50 CAD per K23, and when I got the K26 they were about $8.75 each on Ebay (before shipping).
    Thanks again!
     
  5. Magnus

    Magnus Member

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    Sorry, i have no idea where you'd source bricks in Vancouver. I got mine in Winnipeg where the store had a few boxes of new old stock K26 bricks which were way more robust than the K23 bricks.

    Your local pottery store owner might be able to help if you haven't talked to them yet. A heat treat oven is basically a kiln and they should know how to build a kiln.

    Good luck,
    Magnus
     
  6. dancom

    dancom Dust Maker

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    I posted this on Saturday but the site went down and I think the backup of the database was installed.

    Any additional insulation is a bonus. Insulated Fire Bricks (IFBs) come in different sizes. I used the 2-1/2" thick ones for my oven. This provides good insulation. However, the exterior of my oven will get to 70°C plus after an hour or so. Evidence of heat loss. Although it leaks a bit, it will get to 1070°C in about 90 minutes.

    Adding some 1" ceramic blanket would be speed up the time needed to get to your target temperature and save you money on electricity. Also some lower cost 1-1/4" fireplace bricks from your local hardware store would also help. Make sure they cover the seams of the IFBs. Unlike ceramic wool, these are rigid and a little easier to work with when skinning the oven. The biggest heat loss will be around the door opening. Sand with a block to get a nice flat fit.

    Putting a mortar between the bricks was hit and miss for me. This I learned when taking the roof off to make coil repairs. It wasn't going well as the mortar went all crumbly from the heat. I ended up using the 1/8" steel rod for internal ties. This is basically rod sharpened to a chisel tip and drilled into the centre of the bricks with a drill.

    Hope this helps,

    Dan
     

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